1. Field of the Invention
The present invention relates to a gyro and a method of operating the gyro. More particularly, it relates to a gyro which utilizes a ring resonator type laser.
2. Related Background Art
Heretofore, a mechanical gyro having a rotor or a vibrator, and an optical gyro have been known as gyros each of which is used for detecting the angular velocity of a moving object. In particular, the optical gyro is capable of instantaneous start and has a wide dynamic range, and it is therefore innovating in the field of gyro technology.
Such optical gyros include a laser gyro of ring resonator type, a fiber-optic gyro, a gyro of passive ring resonator type, etc. Among them, a ring resonator type laser gyro employing a gas laser was begun to be developed earliest, and it has already been put to practical use for aircraft etc. Recently, a ring resonator type laser gyro of small size and high precision has also been proposed, and one disclosed in the official gazette of Japanese Patent Application Laid-Open No. 5-288556 is mentioned as an example.
The ring resonator type laser gyro in the prior art is such that a clockwise laser beam and a counterclockwise laser beam are once emitted out of a laser, and that both the laser beams are received by a photodetector, thereby to detect an electrical beat as a signal. Coupling losses are therefore suffered when the laser beams enter the photodetector.
Moreover, noise is induced by light which enters into the laser from reflection points lying outside the laser. In some cases, therefore, an optical isolator must be mounted for the purpose of avoiding the noise.
Further, it is often desired to make the drive system of the ring resonator type laser gyro smaller in size and lighter in weight or to reduce the influence of the noise of the driving power source of the laser gyro on the gyro itself.
An object of the present invention is to provide a gyro and an operating method therefor which are free from or are relieved from such problems as the coupling losses and the optical feedback noise.
Other objects of the present invention are to make the drive system of a ring resonator type laser small in size and light in weight, and to reduce the influence of the noise of the drive system on the ring resonator type laser.
A gyro according to the present invention is characterized by comprising a ring resonator type laser in which laser beams circularly counter propagate each other and whose driving source is a constant-voltage source, a beat signal being detected as a change in a current that flows through the ring resonator type laser.
The current change can be detected as a change in a voltage across a resistor which is connected in series with the ring resonator type laser.
A method of operating a gyro according to the present invention is characterized by comprising the steps of subjecting a ring resonator type laser to constant-voltage drive, and detecting a change in a current which flows through the ring resonator type laser so as to use the change as a signal for finding a magnitude of an angular velocity which has been exerted on the ring resonator type laser.
Further, the present invention is characterized in that the voltage for driving the ring resonator type laser is modulated with a frequency which lies outside a frequency band of the signal.
The present invention is also characterized in that the gyro including the ring resonator type laser is vibrated at a frequency which lies outside a frequency band of the signal, and that the signal is detected synchronously with the vibrations.
A gyro according to the present invention is characterized by comprising a ring resonator type semiconductor laser in which laser beams circularly counter propagate each other, a beat signal being detected as a change in impedance of said semiconductor laser.
Besides, a method of operating a gyro according to the present invention is characterized by comprising the step of detecting a change in impedance of a ring resonator type semiconductor laser so as to use the change as a signal for finding a magnitude of an angular velocity which has been exerted on the ring resonator type semiconductor laser.
More concretely speaking, the change in current and the change in impedance means the change of frequency in current and the change of frequency in impedance, respectively.